Here \(F_\sharp : = |\Re F| + |\Im F|\) . Theoretically, apart from some possible wave numbers, the equation (REF ) is solvable if and only if \(z\in D\) .
This implies that \(I_{FM}(z)\)  is small for \(z\in \mathbb {R}^2\backslash \overline{D}\)  and relatively large for \(z\in D\)  [1]}, [2]}.
